Several risk factors associated with hearing loss (HL) among school age children (6 to 19 years old) in the United States were examined, including: age, sex, ethnicity or race, urban residence, annual family income, and children's general health status. Air-conduction audiometric thresholds were obtained at .5, 1, 2, 3, 4, 6, and 8 kilo- Hertz (kHz) frequencies for 5,915 children in randomly-selected communities for the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994. Pure-tone averages (PTA) based on thresholds at .5, 1, and 2 kHz (lower frequencies), and at 3, 4, and 6 kHz (higher frequencies) were computed for the "better" and "worse" ear responses. Hearing outcomes appropriate for children were defined as: a) PTA less than 15 dB (normal range), b) PTA equal to or greater than 15 dB (slight/mild or greater HL), and c) PTA equal to or greater than 25 dB (moderate or severe HL). Also, multivariately-adjusted odds ratio (OR) estimates of relative risk and 95% confidence intervals (CI) were calculated using logistic regression models. The prevalence of hearing loss equal to or greater than 15 dB in the "better" ear in the low frequencies was 2.1%. The prevalence of HL for Mexican-American children was significantly higher. Also, younger children aged 6-8 years had increased prevalence of HL. The prevalence of HL equal to or greater than 25 dB in the low frequencies was 2.9 per 1,000 children. For children with "fair/poor" general health, this prevalence estimate was significantly increased to 14.6 per 1,000 (OR=5.2; 95% CI, 1.5-18.5). Overall, we found the prevalence of bilateral ("better" ear) low frequency hearing impairment increased with young age, low family income, Mexican- American ethnicity, and fair/poor children?s health status. These findings illustrate the need to identify HL early and develop effective interventions to insure the development of communication skills needed in school and later in life. Additional studies using NHANES III have examined the "reliability" of the hearing threshold determinations and, also, measures obtained to assess the middle ear status (tympanometry and acoustic reflex). We have also begun collaborating with NIEHS and NICHD on a study of in-utero exposure to organo-chlorine compounds in relation to health effects in children, utilizing the U.S. Collaborative Perinatal Project's stored blood specimens and health data, including hearing thresholds obtained on the children at age 8. The Branch has also helped to support an audiological examination and health survey of a random sample of children in Costa Rica, with emphasis on a random sample of second grade students. Preliminary findings from this study were presented at the annual meeting of the American Speech-Hearing-Language Association (ASHA) in Boston. Additionally, we have collaborated with the NICHD Newborn Network on the analysis of children's hearing status at 2 years of age, following treatment in the NINOS clinical trial at birth with inhaled nitric oxide to improve oxygenation and reduce the need for ECMO in near-term hypoxic neonates.